Carbon nanotube (cnt) extrusion methods and cnt wire and composites

ABSTRACT

A method of manufacturing a carbon nanotube (CNT) extrusion. The method includes providing a carbon source, and extruding the CNT extrusion through an extrusion die. The extruded CNT extrusions can be spun into fibers, strands or the like in order to produce a final product. The carbon source can be mixed with a liquid prior to being extruded.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 12/946,331,filed on Nov. 15, 2010, which is a divisional application of U.S.application Ser. No. 11/756,076, filed May 31, 2007, now U.S. Pat. No.7,833,355, which issued on Nov. 16, 2010. The present application alsoclaims priority to U.S. Provisional Application Ser. No. 60/803,740filed Jun. 2, 2006.

TECHNICAL FIELD

The present invention relates to carbon nanotube (CNT) wire andcomposites, and methods for making the same.

BACKGROUND

One of the greatest problems facing space programs has been, andcontinues to be, the cost of putting payloads into space. That cost is adirect consequence of the launch system weight required to get a givenpayload out of the earth's gravity well. With current technology, thatequates to about $25,000 or more for every 1 pound of payload just toget to orbit. Lunar or Mars missions will cost much more.

In an effort to reduce this cost ratio, space agencies have implementedpayload-to-orbit cost reduction initiatives. These initiatives haveincluded several new technologies and demonstrator programs. Theobjective was to bring the payload cost down to $1000/pound or less.However, this objective has proven elusive. For example, testing oflightweight composite tanks indicated that they may not be able to meetlaunch stresses. The conclusion is that the composite strength requiredfor large lightweight tanks is not achievable with present daymaterials. But, these types of tanks will be crucial for reducing liftcost significantly and achieving reasonable Lunar and Mars mission cost.

Also, a big problem facing the automotive industry in its efforts toconvert to hydrogen fuel is how to store large amounts of hydrogen onthe vehicles. A good solution is to compress the hydrogen to very highpressures, over 10,000 psi. But, the safety and reliability of presentday composite fuel tanks at these high pressures is questionable.

There was a new material breakthrough discovery made in 1991 by SumioIijima of NEC Laboratory in Tsukuba Japan, on a new type of carbonstructure called a carbon nanotube (CNT). These tubes actually areabundant in nature and have been around forever. The outstandingproperties of CNT were not realized until Iijima determined that theywere tubular graphene pieces. The carbon bond of graphene (sp²) isstronger than that of diamond (sp³). CNT can now be readily made inlaboratories. A high energy arc through a carbon rod produces carbonsoot, which contains CNT. The significance of the tubular shape is thatthe graphene sheet is rolled into a continuous crystal structure givingit a tensile strength stronger than any other known material. CNT can beover 100 times stronger than steel, with a strength to weight ratio 30times greater then Kevlar. Suddenly, hypothetical structures (like aspace elevator) have become theoretically possible.

Since the discovery of the properties of CNT, there has been an enormousamount of research on CNT and efforts to commercialize it. However, abig drawback to commercial applications is that the tubes can only bemade several micrometers long at best. This short length eliminates thepossibility of spinning or weaving them into optimal fibers or wires. IfCNT wire could be made, it could be woven into composite materials forcomposite tanks and other lightweight structures for space applications.The high tensile strength of CNT wire will allow much greater burstpressure in composite tanks, enabling them to withstand the launchstresses. This same technology can be used to produce the needed veryhigh pressure hydrogen fuel tanks for the automobile industry. Also, CNTwire in struts, beams, and panels will allow lighter and more fuelefficient transportation vehicles like cars, trucks, and planes; willenhance the building industry allowing longer bridges and tallerbuildings; and will greatly enhance military armored vehicles and bodyarmor capabilities.

Presently, CNT made in a controlled manner in industry and laboratoriesis grown. One method now used to grow CNT is to place catalyst dots on abaseplate or substrate. Growth is from the bottom up, as the catalystadds carbon atoms to the tube. One study showed that the catalystclusters actually oscillate from dome to rod shapes and back(shape-shift) as the tubes grow. Historically, the tube's growth stopsafter it becomes a few micrometers long due to the tube's mass exceedingthe catalyst capability.

What is needed then is to produce CNT in continuous extruded wire form,and to weave these wires into fabrics for incorporation into compositematerials, enabling very high strength lightweight fuel tanks,structural members, and armor.

SUMMARY OF THE INVENTION

The present disclosure is directed toward a novel use of the catalystaction of shape-shifting to achieve longer CNT lengths. The methodsignificantly differs from present tube growth methods in that, toproduce CNT wire, an extrusion process is utilized. Present tube growthforming methods result in tubes that are much too short to perform aspinning action to produce a CNT yarn or weaved cable of significantstrength. Even with tubes long enough to spin, the fiber strength willbe limited to the interconnecting bond between tubes. What is needed isa continuous extrusion method of making CNT continuous wire, so that theCNT strength is maintained through the entire length of the wire orcable. But the continuous part of the process needs only be the netresult. That is, a discrete step-by-step oscillator can build on theforming end of a CNT without the physical limits of a catalyst, and thenet result is an endless extrusion.

One embodiment provides that, instead of the catalyst being placed on asubstrate in the form of a dot, it is formed into a tube itself, and theCNT forms as carbon flows through the catalyst tube. In addition, thecatalyst tube is externally controlled and made to shape-shift asrequired to form CNT extrusions. Because it is in the shape of a tube,when it is stretched, its inside diameter will decrease; when it iscompressed, its inside diameter will increase. As carbon is made to flowthrough the tube by an external pressure, the catalyst action of thetube forms the carbon into CNT. The CNT formation plugs the tube, causesa back pressure, and stops the flow of carbon through the tube. However,by forcing the tube to compress, its inside wall will expand, therebyreleasing the formed CNT and backpressure. Then, by quickly stretchingthe tube to close its walls back down before the CNT completely exits,more carbon can build on the back end of the CNT, making it longer withthe same diameter. Repeating this process in an oscillatory manner, tofirst form and then release the CNT, produces a continuous CNT wire outthe end of the catalyst tube.

In one embodiment, a carbon nanotube (CNT) extrusion system includes acarbon source, an extrusion die having a baseplate having a plurality ofdie sets, each die set has a plurality of through-holes in fluidcommunication with the carbon source and a corresponding plurality oftemplate tubes connected at one end to the baseplate and coaxial withthe through-holes, each template tube includes a catalyst for forming aCNT structure in combination with the carbon source. An oscillatingmechanism operatively associated with the free end of each template tubeaxially oscillates the template tubes to alternately form and releasethe CNT structure within each template tube in a continuous manner. Theoscillating mechanism can be an alternating electric field or magneticfield applied to the template tubes, the frequency of the electric ormagnetic field being synchronized with a formation rate of the CNTwithin the template tubes.

In another aspect of the invention, a carbon nanotube (CNT) extrusionsystem, includes a carbon source; an extrusion die having a templatetube in fluid communication with the carbon source, the template tubeincluding a catalyst for forming a CNT structure in combination with thecarbon source; and an oscillating mechanism operatively associated withthe template tube for axially oscillating the template tube toalternately form and release the CNT structure in a continuous manner.The template tube can be at least one of silicon carbide, boron carbide,cobalt, nickel, iron, or carbon. Alternatively, the template tube can bea CNT having a larger diameter than the CNT structure to be formed.

A method of continuously forming a CNT is also provided. The methodincludes providing a source of carbon; providing an extrusion diecomprising a template tube in fluid communication with the carbonsource, the template tube including a catalyst for forming a CNTstructure in combination with the carbon source; introducing the carboninto the template tube to initially form a CNT structure; andthereafter, repeatedly axially oscillating the template tube at afrequency corresponding to a formation rate of the CNT structure toalternately form and release the CNT structure in a continuous manner.The step of axially oscillating the template tube can includeelectrically charging the template tube and applying an externallyoscillating electric field to the template tube such that it tostretches and compresses in an oscillating manner.

The extrusion die can be a stationary first plate and a movable secondplate, with the template tube extending between the two plates, andwherein the step of oscillating comprises oscillating the second plateback and forth with respect to the first plate to alternately axiallycompress and stretch the template tube at a rate synchronized with aformation rate of the CNT within the template tube.

The extrusion die can be made by providing a porous anodic alumina (PAA)baseplate with an etched hole; electrochemically plugging the hole;anodizing nano-channel alumina (NCA) onto the baseplate, using theplugged hole as an alignment template for a second anodizing process;electrochemically depositing a catalyst into the bottom of the NCA hole,on top of the plug; forming the CNT template tube in the NCA hole by achemical vapor deposition (CVD) process; etching out the catalyst andplug to leave a clean through-holes through the PAA baseplate andtemplate tube; and, thereafter, etching away a portion of the NCA suchthat one end of the template tube is connected to and extends from NCAand PAA baseplate, the free end of the template tube capable of beingoscillated.

The resulting continuous extrusions of CNT can be fed into a spinningmechanism to form strands, wire, cable, yarn, fabric or the like. Acombination of continuous extrusions and segments of CNT can also beused to form such structures.

Other advantages and features of the invention will become apparent toone of skill in the art upon reading the following detailed descriptionwith reference to the drawings illustrating features of the invention byway of example.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference shouldnow be made to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of theinvention.

In the drawings:

FIG. 1A shows a schematic diagram of a CNT wire extrusion processaccording to an embodiment of the present invention, while FIG. 1B showsa CNT extrusion during the CNT release state;

FIG. 2 shows a schematic diagram of an individual CNT template stackupwithin the extrusion die during the CNT forming state;

FIG. 3A shows a plan view of a CNT extrusion die with an exemplaryextrusion hole set, while FIG. 3B shows a side sectional view of thedie;

FIG. 4 shows a schematic diagram of a CNT wire extrusion processaccording to an embodiment of the present invention; and

FIG. 5 shows a schematic diagram of a CNT wire extrusion processaccording to another embodiment of the present invention.

DETAILED DESCRIPTION

While the present invention is described with respect to a method andapparatus for extruding CNT to form CNT stranded or solid wire, thepresent invention may be adapted and utilized for creating long-strandCNT for other uses including CNT extrusions spun or woven intofilaments, fibers, strands, strings, rope, cable, yarn, fabric or twine.These materials can comprise continuous extrusion CNT, or long-strandedCNT, or combinations of continuous and long-stranded CNT.

In the following detailed description, spatially orienting terms may beused such as “left,” “right,” “vertical,” “horizontal,” and the like. Itis to be understood that these terms are used for convenience ofdescription of the components or embodiments by reference to thedrawings. These terms do not necessarily describe the absolute locationin space, such as left, right, upward, downward, etc., that any partmust assume.

In the following description, various operating parameters andcomponents are described for several constructed embodiments. Thesespecific parameters and components are included as examples and are notmeant to be limiting.

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIG. 1illustrates a schematic diagram of a CNT wire extrusion processaccording to an embodiment of the present invention. Specifically, FIG.1A shows one example of a CNT extrusion process during the CNT formingstate, and FIG. 1B shows the exemplary embodiment of CNT extrusionduring the CNT release state. The system 10 comprises a plurality ofcatalyst tubes 12 which are each shown connected to a stationarybaseplate 14 at one end, and to a movable plate 16 at the other end. Themovement of the oscillating plate 16, in this example, is controlled bya solenoid 18 operatively connected to a controller 20 which may be asuitable power source 20. The controller may also be a moresophisticated device such as a microprocessor-based controller whichprovides control of the solenoid 18. In such a case, controller 20 mayinclude a microprocessor in communication with input ports, outputports, and computer readable media via a data/control bus. Computerreadable media may include various types of volatile and nonvolatilememory such as random access memory (RAM), read-only memory (ROM), andkeep-alive memory (KAM). These “functional” descriptions of the varioustypes of volatile and nonvolatile storage may be implemented by any of anumber of known physical devices including but not limited to EPROMs,EEPROMs, PROMs, flash memory, and the like. Computer readable storagemedia include stored data representing instructions executable bymicroprocessor to implement the method for CNT extrusion according to anembodiment of the present invention. Controller 20 may communicate withthe various sensors and actuators via an input/output (I/O) interface.Such sensors may include temperature and pressure sensors.

The catalyst template tubes 12 shown are silicon-carbide.Silicon-carbide has been shown to be a good catalyst for growing CNT,and may be a good candidate for a catalyst tube. The catalyst tubes 12can be thought of as templates in this extrusion process. Some othercatalysts used on plates have been cobalt, nickel, and iron, all ofwhich may possibly be used in making the templates. Because of thecarbon-carbon bond length, boron and silicon fit best within thegraphite hexagonal structure, making them very good template ingredientcandidates.

In operation, the oscillating action of the plate 16 relative to thestationary plate 14 results in the template tubes 12 being compressedand opened (FIG. 1B), while the movement of the plate 16 apart from thestationary plate 14 results in the template tubes being stretched, orelongated, and closed (FIG. 1A). The stationary plate 14 and theoscillating plate 16 each have a plurality of through-holes 22, 24. Eachtemplate tube 12 is attached at one end to an opening 22 in thestationary plate, and attached at the other end to an opening 24 in theoscillating plate. The through-holes 22 of the first plate 14 areco-axial with the through-holes 24 of the second plate 16. Thethrough-holes in the first plate 14 allow the flow of carbon vaporthrough the template tube 12 in a controlled manner.

FIG. 1A shows the oscillating mechanism as a solenoid 18 havingelectromagnetic coils 26 and springs 28 being employed to move thesecond plate 16 back and forth with respect to the first plate 14 by wayof a control rod 30. However, in practice the oscillating mechanism cancomprise any number of more robust mechanisms on a microscopic level.For example, the movable second plate 16 can be permanently magnetizedwith a ferrous doping, and an oscillating magnetic field applied upon itto get it oscillating at the proper frequency for the extrusion processto take place.

As the carbon vapor passes through the first plate 14 and into thecatalyst template tube 12, the carbon bonds to form a CNT extrusion 32.As carbon in the form of vapor is made to flow through the template tube12 by an external pressure, the catalyst action of the template tube 12forms the carbon into CNT. The CNT formation plugs the template tube 12,causes a back pressure, and stops the flow of carbon through thetemplate tube 12. However, by forcing the template tube 12 to compressby movement of the second plate 16 towards the first plate 14, theinside wall of the template tube 12 will expand, as shown in FIG. 1B,thereby releasing the formed CNT and backpressure. Then, by moving thesecond plate 16 away from the first plate 14, the template tube 12 isquickly stretched, thereby closing its walls back down before the CNTcompletely exits. As a result, more carbon can build on the back end ofthe forming CNT, making it longer and with the same diameter. Repeatingthis process in an oscillatory manner, to first form and then releasethe CNT, produces a continuous CNT 32 out the end 34 of the catalysttemplate tube 12. Thus, the spinning mechanism 40 can be any one of theknown forms for creating such structures from single strands which, inthis case, are CNT extrusions.

Once formed, the CNT extrusions 32 can be fed into a spinning mechanism40 or the like to braid or otherwise twist the strands 32 into a bundleof strands. The CNT extrusions 32 can be spun or woven into any numberof known forms such as twisted pairs, braided CNT, bundles, filaments,fibers, strands, strings, rope, cable, yarn, fabric or twine. Theseforms can be further woven into fabrics or the like.

To facilitate the growth of the catalyst template tubes 12, a scaffoldstructure can first be made on the baseplate 14. The composition of thescaffold has a natural tendency to attract and bind the desired catalystmaterials in the proper lattice configuration. One method of building awire scaffold uses genetically engineered viruses that bind zinc orcadmium sulfide particles linearly to the outside surface of the virus,forming a wire structure. The organic material of the virus can then bethermally or chemically etched away, leaving the desired catalyst tubestanding.

An alternative form of the catalyst template tube 12 follows. It is alsoknown that CNT forms in different layers, making multi-walled CNT. Thispermits an alternate template tube, in the form of a larger CNT itself.Once a CNT starts to grow, additional layers of CNT can form over itspontaneously. Any solidifying element on a surface tends to arrange inaccordance with the surface crystal lattice, if possible. By making thesurface crystal lattice graphene, the solidifying carbon would fitperfectly into it, and also form a graphene face. Therefore, to make thetemplate tubes 12, CNT can simply be grown as is normally done off anappropriate baseplate 14.

The catalyst template tubes 12 must be attached to each of the firstplate 14 and second plate 16. The attachment bonding must be such thatthe template tubes 12 remain attached during extrusion oscillations ofthe tubes, however, the attachment bond depends largely on the catalystused for CNT growth. Also needed, is a method to make the through-holesin the baseplate in alignment with the tubes themselves. In addition, inorder to form real world manageable size wires, enough CNT wire standsshould be extruded simultaneously from a single baseplate extrusion dieforming macro-size wire strands (the typical CNT is a few nanometers indiameter).

One solution uses either electronic photolithography methods, or ahighly controlled anodizing process, for deposition of catalyst dots andetching of through holes to form millions of extrusion tubes on a singlebaseplate 14 of similar size and length. One example of the anodizingmethod uses an aluminum baseplate and a cobalt catalyst. A nano-channelalumina (NCA) can be formed on an aluminum substrate by an anodizingmethod, and a cobalt catalyst is deposited in the NCA holes where CNTwas subsequently grown. This process is taken further in this disclosurefor the purpose of forming an extrusion die.

Accordingly, FIG. 2 shows a schematic diagram of an individual CNTtemplate stackup within the extrusion die 110 during the CNT formingstate. Thus, FIG. 2 represents a detail of one template tube 124 withina die 110 having a plurality of template tubes. In this example, a 50 nmthrough-hole 112 results in an approximately 40 nm CNT diameter at thedie exit 114. In an initial step, the aluminum baseplate 116 is preparedby making through holes in it by using a Porous Anodic Alumina (PAA)template method and ion etching. In this example, the PAA preparedbaseplate 116 with through-holes is approximately 1000 nm thick. In anext step, the holes 112 are electrochemically plugged with a nickelplug 118. The NCA 120 is then anodized onto the baseplate 116, using thenickel plugged holes 118 as an alignment template for the secondanodizing process. The starting thickness of the NCA in this example isabout 1000 nm, and includes a plurality of holes 113 aligned with theholes 112 formed in the baseplate 116. In a next step, a cobalt catalyst122 is then electrochemically deposited into the bottom of the NCA holes113, on top of the nickel plugs 118 in the baseplate openings 112. Then,the CNT template tubes 124 are formed or grown in the NCA holes 113 by astandard Chemical Vapor Deposition (CVD) process utilizing the cobaltcatalyst 122. Next, the cobalt catalyst 122 and nickel plugs 118 arethen etched out of the holes 112, 113, leaving clean through holesthrough the aluminum baseplate 116 and CNT template tubes 124. Tocomplete the die fabrication, the NCA 120 is ion etched down to anappropriate height 126, so that the CNT template tubes 124 are nowfree-standing from the baseplate 116 and remaining NCA 128. The templatetubes 124 are free to be oscillated for the extrusion process. In thisexample, the NCA was etched down from 1000 nm to approximately 500 nmafter the template tube 124 was grown. The remaining portion 128 of NCAleft on the baseplate, retains and bonds the CNT template tubes 124 tothe baseplate 116, and can act as a good thermal insulator. For example,approximately 250 nm of NCA 129 aides in retaining the template tubes124, while approximately another 250 nm of NCA 130 was used to aide inproviding catalyst for CNT template tube growth. Additional layers canbe deposited on the NCA after it is etched down. A thin insulator layer132 and an aluminum coldplate 134 can be CVD deposited on top of thesurface of the NCA 128. The coldplate layer 134 is used to thermallycontrol the carbon condensation rate within the CNT template tube duringthe extrusion process.

FIG. 3A shows a plan view of the complete die 110 of FIG. 2; and FIG. 3Bshows a side sectional view of the die 110 of FIG. 3A along sectionlines B-B. The die 110 has seven 50 μm diameter extrusion hole sets 111in a hexagonal pattern. Of course, more or fewer extrusion hole setscould be used. As well, any number of 50 nm holes 112, 113 could be ineach hole set 111. In this example, each hole set 111 contains about200,000 extrusion holes 112, 113 with a 50 nm template tube 124 insideeach. Each hole produces a 40 nm diameter CNT strand through thetemplate tubes 124. The strand diameter depends on the template tubediameter opening. Thus, openings larger or smaller than 50 nm could alsobe used. This configuration of seven holes sets 111 with hundreds ofthousands of extrusion holes each, will produce a multi-stranded CNTwire of about 0.15 mm diameter from a single extrusion die 110 which isapproximately 8 mm square. Larger or smaller diameter wires can be madeby simply adding or subtracting hole sets in the extrusion die. A singlehole set will produce a stranded wire of about 50 μm diameter, which isseveral times thicker than a human hair. Adding multiple extrusion diesto the vapor chamber wall will enable even larger diameter wires andcables.

FIG. 3B shows a side sectional view of the die 110 of FIG. 3A. TheFigure shows the baseplate 116, etched NCA layer 128, insulator 132 andcoldplate 134. The template tubes (not to scale or number) 124 can beseen to extend from the die 110. The thickness of the baseplate abovethe hole sets, NCA layer, Insulator, and coldplate stack-up (1.7 μm) isalso indicated relative to the over-all die thickness (2 mm), as well.Again, these specific numbers are merely an example. They are notintended to be limiting. Recesses 135 are also provided in the interiorsurface 136 of the die 110 for passing carbon vapor to the templatetubes 124 for CNT growth. Again, the configuration shown is merely oneexample of a die 110 according to the present invention. It is not meantto be limiting.

The following describes one example of a process for forming a highlyordered porous anodic alumina (PAA) mask on an aluminum baseplate for aCNT extrusion die with reference to FIGS. 2 and 3. The process starts bypreparing an aluminum extrusion die baseplate sized for the desired CNTmulti-strand wire extrusion diameter. In the example of FIG. 3, a 2 mmthick by 8 mm square plate is suggested for a 0.15 mm multi-strand wire.The baseplate should be high purity (99.999%) aluminum. A number ofrecessed holes, called the hole set 111, are drilled, milled, or etchedout (not to break through) in a pattern that matches the desired wirecross-sectional stranding pattern on the rear side (inside) 136 of thebaseplate 116. FIG. 3 shows seven holes 111 in a hexagonal pattern. Therecess holes can be to a depth of about 1.0 μm from breaking through,with the bottoms 137 as flat as possible. The recess holes should be bigenough to accommodate several thousands of extrusion tube holes 112, 113to be added later (about 200,000 is suggested), but small enough tomaintain the structural integrity of the aluminum baseplate for handlingthe process temperatures and pressures, with ample wall thicknessbetween the recess holes. In the example of FIG. 3, the holes 111 areabout 50 μm in diameter with at least 50 μm wall thickness between theholes 111.

Next, the aluminum baseplate is degreased in trichloroethylene, etchedfor 1 minute in a sodium carbonate solution (25 g/L) at 80° C., rinsedwell in distilled water and immersed in 1:1 v/v nitric acid for 20seconds at room temperature to neutralize any residual carbonate. Afterrinsing in triply distilled water, the baseplate is electropolished in aperchloric acid (60%) in ethanol solution (1:4 by volume). Anodizationon the baseplate is carried out in a thermally insulated electrolyticcell with 40 V DC applied to a 0.25 M aqueous oxalic acid electrolytefor 15 hours at 10° C. The electrolyte should be vigorously stirredduring anodization in order to maintain temperature and electrolyteconcentration uniformity. This process will result in a PAA film on topof the baseplate 116 approximately 81 μm thick. The long anodizationtime in this step allows for self-organization of the oxide to formhighly regular aluminum pores in the baseplate. The pore diameters are afunction of the anodizing voltage, and they can be varied from five tohundreds of μm wide, (the given parameters in these steps produce 40 μmwide pores). The pore diameters dictate the PAA mask hole diameters tobe produced in the next step, which then dictate the diameter of theion-milled holes 112 through the baseplate. The baseplate ion-milledholes 112 will later enable the Nano-Channel Alumina (NCA) hole 113alignment.

In a subsequent step, the thick PAA film is stripped off by immersingthe baseplate in a solution of phosphoric and chromic acids, leavingbehind an aluminum surface textured with a hexagonal scallop pattern of40 nm wide pores. This is followed by a second anodization step carriedout under the same physical and electrochemical conditions used to formthe first PAA film. The second anodization is carried out for asufficient length of time to grow a film 1.0 μm thick. A highly regularand periodic PAA pattern is formed in this second anodization step, doto the highly regular aluminum pores left by the first anodizationprocess acting as a template for the second anodization. This PAApattern is used as a contact mask for the ion milling process.

The following describes an example of a process for ion milling of thealuminum baseplate, using the PAA mask from the previous step. Ionmilling is a process of etching ballistically through a contact maskusing highly collimated, high-energy particles such as Ar+ ions. Thealuminum baseplate with its PAA film is mounted on a water-cooled copperblock using 0.15 mm thick indium foil to improve thermal contact. Theassembly is placed in a vacuum chamber and evacuated to 5×10⁻⁷ mbar. Theion milling source uses a Chordis high current ion source (such as aDanfysik, model 920-2) operating with Ar+ accelerated through 25 kV andwith an ion current of 13-15 mA. A ˜2 cm diameter ion beam is directednormal to the surface of the PAA film.

The aluminum baseplate is ion milled through the PAA mask, until holesbreak through the thin bottom layers of the recess holes 111 made in thefirst step. The milling will take several minutes. Milling too fast byapplying too much energy will melt the aluminum, and cause it to wet upthe PAA mask plugging the holes. A 7 minute milling time at least issuggested. The diameter of the finished ion milled holes should be atleast 50 nm, but should not break through to adjacent holes. That is,sufficient wall thicknesses should remain between the holes 112. The 1μm PAA hole, plus the 1 μm aluminum hole to be milled, gives a 2 μm deepthrough-hole total. With a starting hole of 40 nm diameter, the holeaspect ratio is 2/0.04=50, which is sufficient for the milling exhaustrequired.

The ion milled holes 112 in the baseplate now need to be plugged 118 atthe top, so that a CNT catalyst can be deposited later into the bottomof the Nano-Channel Alumina (NCA) holes 113 yet to be formed. Theremaining PAA mask after ion milling can now be used as a plugdeposition mask. In this step, nickel is electrochemically depositedinto the aluminum holes, so that an approximately 100 nm long nickelplug 118 forms just at the top of the holes 112, with a good portion ofthe plug extending up into the PAA mask (about 50% is suggested). Thenickel protrusions into the PAA will also act as a alignment templatefor the NCA deposition process. A chemical etch can then be used toremove the PAA mask and any residual aluminum oxide without affectingthe underlying aluminum baseplate or nickel plug. Again, a mixture ofphosphoric and chromic acids can be used. The baseplate is now ready forthe next step. The following describes a process for forming alignedNano-Channel Alumina (NCA) on the baseplate. Using the nickel pluggedaluminum baseplate from the last step, the top surface is anodized usinga 0.3 M oxalic acid solution at 15° C. under a constant voltage of 40volts, until a 1 μm thick NCA film is formed. The nickel plugprotrusions from the baseplate will cause the NCA holes to be perfectlyaligned with the baseplate holes. Again, the applied voltage controlsthe NCA hole diameters, and they should be made 50 nm wide in thisexample.

The following describes a process for forming carbon nano-tube (CNT)extrusion tubes 124 in the NCA Array. The process continues byelectrochemically depositing approximately 100 nm long cobalt catalyst122 in the bottom of the NCA holes 113, on top of the nickel plugs 118.The bottom side of the baseplate is masked off at this time.

The carbon nanotubes are then grown by first reducing the catalyst byheating the cobalt-loaded NCA and baseplate in a furnace to 600° C. for4 to 5 hours under a CO flow of 100 cm³/min. The CO flow is thenreplaced by a mixture of 10% acetylene in nitrogen at a flow rate of 100cm³/min. The acetylene flow is maintained for 2 hours at 650° C. Then,the extrusion die sample is annealed in nitrogen for 15 hours at 650° C.

Next, both the cobalt catalysts 122 and the nickel plugs 118 arechemically etched out of the holes 113 from the top side of the NCA 120,using the NCA as an etch resist protecting the aluminum. The cobaltcatalyst is etched out first using HCL, followed by etching out thenickel plug using HN03. A slight etch-back of the aluminum holes isacceptable, since the diameter the aluminum holes in the baseplate isnot critical.

Now that clear straight through holes have been established through theCNT template tubes 124 and baseplate, the NCA 120 needs to be etch downso the CNT tube ends are free to be oscillated during the extrusionprocess. The NCA is etched down 500 nm, using a mixture of phosphoricand chromic acids to result in the thicknesses shown at 128.

Next, the insulating film 132 and cold plate 134 are formed. Using achemical vapor deposition process, a 100 nm thick insulating film isdeposited on top of the NCA surface. During this step, the top of theCNT template tubes should be masked off. Then, on top of the insulationlayer 132, a 100 nm thick aluminum film 134 is electrochemicallydeposited, to be used as a CNT wire extrusion cooling plate. The CNTwire extrusion die 110 is now complete, and ready for installation intothe extrusion jig 190 which is described in greater detail with respectto FIG. 4.

FIG. 4 shows a schematic diagram of a CNT wire extrusion systemaccording to an embodiment of the present invention. In this example,the extrusion die 110 is clamped to a CVD pressure chamber 200 wallorifice using coupling mechanism 216. An electric coil 202 is providedto magnetically couple the template tubes 124 of the die 110 with aperpendicular magnetic field relative to the axial orientation of thetemplate tubes. The CNT extrusion flow through the template tubes of thedie 110 is maintained by the pressure within the carbon vapor chamber200. The pressure is adjusted by a pressure regulator 204 to control theflow rate of carbon during the template tube release cycle. A lineheater 208 is coupled to the carbon source feed line in order topre-heat the carbon source gas, such as methane for example, beforeentering the CVD chamber 200. A chamber heater 206 is coupled to the CVDchamber 200 in order to assure a carbon vapor is established, and toaccurately control the operating temperature of the chamber 200 vaporduring the extrusion process. To assist the CNT flow through thetemplate tube, a second, strong magnetic field may be applied by anotherelectric coil 203 in the axial direction of the CNT extrusion flow. Thisassist process requires a doping of the CNT wire extrusion with iron orferrous particles, or similarly ferromagnetic phase particles at thecondensation temperature within the template tube condensation section.In addition to assisting flow control, the magnetic field can also helpprevent the extruded CNT wire strands from curling and clumping uponexiting the extrusion template tubes.

The CVD pressure chamber 200 is attached by coupling mechanisms 216 to atemperature control housing 205 that encloses the CNT wire extrusion asit exits the extrusion die 110. This housing 205 has itself an openingfor the exit of the CNT extrusion wire, but can contain any desired ionsolution or temperature controlled fluids or gases in support of theextrusion process when properly orientated. The primary purpose of thehousing 205 is to provide a controlled temperature environment on theexit surface of the extrusion die 110. Actively controlling the housingenvironment temperature is a housing heater 207, a nitrogen feed lineheater 209, and a chiller device 214. The chiller 214 can be made tochill nitrogen, for example, as it is fed from the nitrogen feed line210 through valve 211. Alternatively, the chiller can be made tocirculate a retained fluid in the housing 205 in order to maintain acontrolled environment temperature. A nitrogen purge line 212 is alsoconnected to the CVD chamber 200 with an inline control valve 213 andnitrogen feed line heater 201.

The baseplate 110 is mounted to the pressure chamber 200 so that thecarbon can flow through the plate holes and into the template tubes. Theother end of the template tubes are thus free to be stretched orcompressed by external forces. The carbon pressure is low initially sothat the carbon deposits onto the inside walls of the template tubesforming CNT structures, which will subsequently plug the template tubescausing a back pressure. The pressure in the chamber 200 is then raisedand the CNT plug is released by compressing the template tubes to makethe inside diameter of the tubes bigger. The CNT plugs will then beginto move out of the tubes. By quickly stretching the template tubes againand closing the inside diameter back down, the CNT extrusions stopmoving and form longer at the trailing ends toward the extrusion die110. This process of stretching and compressing the tubes is repeated inan oscillatory manner so that CNT wire is extruded out the ends of thetubes. The frequency of oscillation is made to match the flow rate withthe formation rate. The flow rate is a function of chamber pressure andmagnetic assist field strength, and the formation rate is a function ofcondensation parameters. The length of the CNT extrusions is onlylimited by the desired reel size. The process can create extrusions ofcarbon nanotube of various chiral shapes, including zigzag and armchair,or any combination of chiral shapes. Additionally, the extrusions ofcarbon nanotube can be single-wall or multiple-wall structures in anycombination of chiral shapes.

The following describes one example of a CNT extrusion process forforming CNT wires of any desired length with reference to FIG. 4.

In a first step, a CNT extrusion die 110 is mounted onto the ChemicalVapor Deposition (CVD) chamber 200, covering the extrusion orifice ofthe chamber, using 2 set screws 216 sufficiently torqued to preventleakage of the carbon vapor through the contact surface.

The CVD chamber 200 and temperature control housing 205 is then purgedusing the nitrogen lines 210, 212 for several minutes. While maintaininga reduced purge flow, the nitrogen lines, carbon source line, CVDchamber, and housing are preheated to 600 C using heaters 201, 209, 208,206, and 207. Then, the CVD chamber 200 and housing 205 temperatures areraised to 650 C using heaters 206 and 207. Next, the carbon source(acetylene for example) is allowed to flow into the CVD chamber 200while stopping the purge flow into the CVD chamber using valve 201, andmaintaining the housing nitrogen flow through the chiller device 214 at650 C using line heater 209. The CVD chamber and housing temperaturesare maintained at 650 C, ensuring that a good carbon vapor isestablished, and that the vapor is flowing freely though the extrusiontubes.

In a further step, the housing 205 nitrogen temperature is reduced usingthe combination of the housing nitrogen line heater 209, the housingheater 207, and the chiller 214, until the carbon vapor condenses withinthe extrusion template tubes 124, plugging the tubes and completelystopping the flow out of the tubes. The housing temperature and thenitrogen flow are maintained into the housing at this establishedtemperature.

The CVD chamber 200 pressure is then increased until about 10 nN isapplied to the carbon plugs within the extrusion tubes 124 using thecarbon source pressure regulator 204. The carbon plugs are not blown outat this point. If they blow out, the pressure should be decreased toallow new plugs to form.

In a further step, an AC current is applied to the electric couplingcoil 202, generating an alternating coupling magnetic field with theextrusion tubes. The AC current starting frequency can be set to 530kHz, the first harmonic of CNT. The current in the coil is thenincreased from 0.0 amps until the magnetic field produces about 100 nNcompression force on the extrusion tubes 124. This force will compressthe tubes 124 approximately 50 nm, opening the inside diameter about 2nm, which is sufficient to break the van der Waals forces, releasing theCNT formed plug in the extrusion tube. The extrusion tube 124 can bestretched back out by reversal of the magnetic coupling, capturing theback portion of the CNT plug before it exits the condensation area ofthe tube, stopping the flow and allowing additional condensation ofcarbon to form longer CNT. The cycle repeats at the give frequency ofthe coupling coil 202 AC current. If the CNT is not forming in pace withthe extrusion frequency, causing brakes in the extrusion, the CVDchamber 200 pressure can be decreased or the housing 205 temperature canbe decreased, or any combination of both. Once a continuous flow of CNTwire extrusion is established, the coupling frequency can be increasedwhile adjusting the CVD chamber pressure and housing temperatures tomaintain a continuous extrusion is highly desirable, since a higherfrequency will produce greater lengths of wire in shorter time. If 50 nmof CNT is formed each cycle, then at 530 kHz, 0.0265 meters of CNT wirewill be produced per second (95.4 meters/hour).

The process of attaching the outer ends of the grown extrusion templatetubes to an oscillation plate can pose difficulties. Since many of thedie fabrication processes require unobstructed access to the baseplateand NCA, the oscillation plate needs to be attached to the extrusiontemplate tubes after they are grown and dangling. However, it ispossible to eliminate the need for the second movable oscillation platealtogether. It has been shown that the ends of CNT are frayed to someextent, and that these frayed ends accumulate large electron charges.These charges, if held in place, can be used themselves to stretch andcompress the template tubes. In addition, it has been shown that byimmersing the tubes in a saltwater solution and applying an electriccharge to the tubes, the tubes will also expand axially. The chlorineions bind to the tubes when positively charged, and the sodium ions bindwhen negatively charged. The binding atoms cause electron displacementon the tubes, causing the tubes to contract and stretch. Thedisplacement and stretching is much greater with a positive chargeapplied than a negative one. Therefore, by applying an oscillatingelectric charge to the baseplate, the attached tubes will likewise becharged, and stretch and compress along with the oscillating charge.Other possibilities would be to dope or bond other elements to the CNTto establish a charge throughout the template tube length.

FIG. 5 shows a schematic diagram of a CNT wire extrusion processaccording to another embodiment of the present invention. Along withapplied charge control, it has been demonstrated in electronic memoryformation processes that applied fields can also cause the CNT tostretch and bend. In FIG. 5, a combination of applied charge and fieldeffects is shown. The stationary baseplate 310 having through-holesprovides carbon vapor to the template tubes 324. A salt solution is usedto provide additional ions to the walls of the template tubes 324. Sincethere is a naturally occurring negative charge build-up on the tube tips325, the solution is made negatively charged and the baseplate 310 ispositively charged by way of a power source 314. This will cause thesodium ions to be drawn to the walls of the template tubes 324 tocomplement the charged tips 325. Making this charge condition staticusing a DC source 314, an alternating current 315 in alignment with thetube axis will create an alternating magnetic field perpendicular to theaxis of the tubes 324. The coupling between the alternating magneticfield and the static electric charge imposes an electromotive force onthe template tubes 324, causing them to stretch and compress axially intune with the frequency of the AC source 315. The proper oscillationfrequency in conjunction with the carbon vapor pressure, will cause thecarbon exiting the template tubes to form a CNT wire extrusion in a formand release manner as described above.

The forgoing processes can provide CNT in lengths in excess of 100 μm.Indeed, much longer, even continuous, CNT structures are possible by theforegoing processes. Continuous lengths of CNT wire extrusions can bewoven into a fabric which then can be incorporated into compositematerials. The composites comprising carbon nanotube segments,extrusions, or continuous extrusions in the form of filaments, fibers,strands, strings, wires, twine, and yarns can be further bonded togetherby radiation hardening methods. Because of the continuous strands ofextremely high tensile strength wire running through the composites,they will be much stronger than any previously made. These newcomposites then can be used to build high strength, high pressure, lightweight fuel tanks and structural components for new space launchvehicles, space transport vehicles, or any other structures. These newmaterials, of course, can also be used in the aviation industry, makinglighter faster and more fuel efficient airplanes and jetliners. Inaddition, the military can use these new materials to make much strongerand lighter armor for armored vehicles and body armor. The automotiveindustry can use the new materials for lighter and more fuel efficientcars and trucks, and fabricate very high pressure hydrogen storagetanks. The CNT wire can be used simply as wire for making the strongestcables ever made, for use in suspension bridges for example. Also, CNTwire properly formed can have conductivity 1000 times greater thencopper, revolutionizing the power industry with many times smaller andlighter electric motors and power cables. Numerous other possibilitiesexist for materials fabricated from the CNT extrusion process of thepresent invention.

Thus, while the invention has been described in connection with one ormore embodiments, it should be understood that the invention is notlimited to those embodiments. For example, the template tubes can bemade of any suitable material for forming carbon nanotubes, includingsilicon carbide, boron carbide, or any combination of proven catalystmaterials such as cobalt, nickel, iron, carbon, or simply a largercarbon nanotube. In this regard, the invention covers all alternatives,modifications and equivalents as may be included within the spirit andscope of the appended claims.

1. A method for manufacture of a carbon nanotube (CNT) extrusioncomprising: providing a carbon source; extruding the carbon sourcethrough an extrusion die; spinning the extruded CNT to form a product.2. A method according to claim 1 wherein the final manufactured productis selected from the group comprising a wire, a string, a rope, a cable,a yarn, a twine, a fabric, a filament, a plurality of filaments, afiber, a plurality of fibers, a strand, a plurality of strands, orcombinations thereof of two or more of said products.
 3. The methodaccording to claim 1 further comprising providing an extrusion diecomprising at least one die member having a plurality of through-holesin fluid communication with the carbon source.
 4. The method accordingto claim 3 further comprising providing a plurality of template tubesconnected at one end to said extrusion die and coaxial with thethrough-holes.
 5. The method according to claim 4 further comprisingproviding an oscillating mechanism operatively associated with the freeend of each plurality of template tubes.
 6. The method according toclaim 5 further comprising the step of axially oscillating the free endof each of said plurality of template tubes.
 7. The method according toclaim 5 wherein said oscillating mechanism comprises an alternatingelectric field or magnetic field applied to said template tubes.
 8. Themethod according to claim 7 further comprising the step of synchronizingthe frequency of said electric field or magnetic field with theformation rate of the CNT extrusion within said template tubes.
 9. Themethod according to claim 4 wherein said template tubes comprise of atleast one of the following group of materials: silicon carbide, boroncarbide, cobalt, nickel, iron, or carbon.
 10. The method according toclaim 4 further comprising the step of providing the template tubes witha diameter greater than the CNT extrusion which is being manufactured.11. The method according to claim 1 further comprising the step ofincluding a catalyst working with said carbon source.
 12. The methodaccording to claim 11 further comprising the step of connecting at leastone template tube to said extrusion die and introducing said carbonsource into said template tube.
 13. The method according to claim 12further comprising the step of repeatedly axially oscillating the atleast one template tube at a frequency corresponding to a formation rateof the CNT structure.
 14. The method according to claim 1 wherein saidextrusion die comprises a stationary first plate and a movable secondplate.
 15. The method according to claim 14 further comprising providingat least one template tube extending between said first plate and saidsecond plate.
 16. The method according to claim 15 further comprisingthe step of oscillating said second plate to alternatively axiallycompress and stretch said at least one template tube.
 17. The methodaccording to claim 15 wherein the oscillation rate is synchronized witha formation rate of the CNT extrusion within said at least one templatetube.
 18. The method according to claim 1 wherein the carbon sourcecomprises a carbon vapor.
 19. The method according to claim 1 whereinthe extrusion die contains a plurality of through holes and a pluralityof CNT extrusions are formed.
 20. The method according to claim 19wherein at least two of said plurality of CNT extrusions are subjectedto said spinning step and are formed into the manufactured product. 21.The method according to claim 20 wherein said manufactured product isselected from the group comprising a wire, a string, a rope, a cable, ayarn, a twine, a fabric, a filament, a plurality of filaments, a fiber,a plurality of fibers, a strand, a plurality of strands, or combinationsthereof of two or more of said products.
 22. The method according toclaim 1 wherein said carbon source is formed by a chemical vapordeposition (CVD) process.
 23. The method according to claim 22 furthercomprising the use of a catalyst in the CVD process.
 24. The methodaccording to claim 1 further comprising extruding a plurality of strandsof CNT extrusion from said extrusion die.
 25. The method according toclaim 24 when said plurality of strands are spun by said spinning stepinto a final manufactured product.
 26. The method according to claim 25wherein said manufactured product is selected from the group comprisinga wire, a string, a rope, a cable, a yarn, a twine, a fabric, afilament, a plurality of filaments, a fiber, a plurality of fibers, astrand, a plurality of strands, or combinations thereof of two or moreof said products.
 27. The method according to claim 24 wherein at leasttwo of said strands are formed in substantial axial alignment with theflow of CNT extrusion.
 28. The method according to claim 24 wherein saidplurality of strands are formed in substantial axial alignment with eachother.
 29. The method for manufacture of a carbon nanotube (CNT)extrusion comprising: providing a carbon source; and extruding thecarbon source through an extrusion die; wherein CNT extrusions areformed.
 30. The method according to claim 29 further comprising the stepof spinning the extruded CNT extrusions to form a product.
 31. Themethod according to claim 29 wherein the final manufactured product isselected from the group comprising a wire, a string, a rope, a cable, ayarn, a twine, a fabric, a filament, a plurality of filaments, a fiber,a plurality of fibers, a strand, a plurality of strands, or combinationsthereof of two or more of said products.
 32. The method according toclaim 29 further comprising providing an extrusion die comprising atleast one die member having a plurality of through-holes in fluidcommunication with the carbon source.
 33. The method according to claim29 further comprising the step of including the carbon source in aliquid prior to extrusion.
 34. The method according to claim 29 furthercomprising extruding a plurality of strands of CNT extrusion from saidextrusion die.
 35. The method according to claim 34 when said pluralityof strands are spun by said spinning step into a final manufacturedproduct.
 36. The method according to claim 35 wherein said manufacturedproduct is selected from the group comprising a wire, a string, a rope,a cable, a yarn, a twine, a fabric, a filament, a plurality offilaments, a fiber, a plurality of fibers, a strand, a plurality ofstrands, or combinations thereof of two or more of said products.